
v^* 



rtV A .V . » • • r <> \> 



^'' 






_,.'"-*,* 




V' 







0' -^ ^..,.' ^x- 



q.. *.. 



57 o S ^/^ 
































V^*rr,'' ..x^ 










> 



RESISTANCE OF THE ROOTS OF SOME FRUIT 
SPECIES TO LOW TEMPERATURE 



A THESIS 



PRESENTED TO 

THE FACULTY OF THE GRADUATE SCHOOL OF CORNELL UNIVERSITY 

FOR THE DEGREE OF DOCTOR OF PHILOSOPHY 



X.. BY 
D. Bf CARRICK 



PUBLISHED AS CORNELL UNIVERSITY AGRICULTURAL 
EXPERIMENT STATION MEMOIR 36. JUNE 1920 



^^'^<i 

o^^ 






1Z^ 



k^ 



CONTENTS 

PAGE 

Review of the literature 613 

Method used in freezing the roots 616 

Results of the experiments 618 

Resistance of apple roots to low temperature 618 

Resistance of pear roots to low temperature 624 

Resistance of Elberta peach roots to low temperature 627 

Comparative resistance of Mazzard and Mahaleb cherry roots to 

low temperature 629 

Resistance of Myrobalan plum roots to low temperature 632 

Resistance of the roots of six grape varieties to low temperature . . 633 
Resistance of blackberry, dewberry, and red raspberry roots to low 

temperature 637 

Resistance of gooseberry and currant roots to low temperature . 6Si 
Sap concentration of American and French apple seedlings and Wilder 

currant as measured by the freezing-point depression 642 

Effect of rapid temperature fall on the freezing of apple roots 64c 

Effect of rate of thawing on the freezing of roots 64^ 

Injury to apple roots when frozen in soil, in water, and in paraffin. . . 64( 
Influence of the scion on the hardiness of one-year roots of the stock. 646 
Effect of sugar solutions, water, and drying out, on the resistance of 

apple roots to freezing 653 

Summary 656 

literature cited 660 



609 



RESISTANCE OF THE ROOTS OF SOME FRUIT SPECIES 
TO LOW TEMPERATURE 



RESISTANCE OF THE ROOTS OF SOME FRUIT SPECIES 
TO LOW TEMPERATURE! 

D. B. Carrick 

There are several types of winter injury to fruit plants which are of 
more or less frequent occurrence in New York State. Among these may 
be mentioned injury to small twigs, especially those of peach trees and of 
tender apple varieties such as Tompkins King; injury to the winter buds 
and sometimes to the blossoms; sun-scald, and the rather closely related 
forms of crotch injury and crown rot; and injury to the roots. Perhaps 
the killing of the roots by low temperature should be associated with the 
less serious types of winter injury in this State, due in part to the fact 
that it occurs in restricted areas. Yet in the Champlain Valley and in 
the upper Hudson River section, the freezing of the roots is one of the 
important problems in fruit production. This is also the case in parts of 
New England, in Canada, and in a number of the Western States. 

The work reported in this paper was begun in the fall of 1915 and^ 
extended thru the spring of 1917. An attempt has been made to determine 
approximately under standard conditions the range of variation and the 
relative hardiness of some of the more commonly grown fruit stocks, 
including a few varieties of the small fruits. Some data were also obtained 
regarding the influence of certain factors on the freezing to death of 
plant tissue. 

Careful field studies and the testing of possible fruit stocks capable of 
withstanding severe cold are significant aspects of the question that have 
not been attacked. It is hoped, however, that some of the results pre- 
sented here may be suggestive in the working out of these other phases of 
the problem of root injury by low temperature. 

REVIEW OF THE LITERATURE 

Craig (1900) observed extensive winter injury to the roots of apple, 
plum, and cherry in Iowa. The one- and two-year-old apple trees in the 

1 Also presented to the Faculty of the Graduate School of Cornell University, in August, 1917, as 
a major thesis in partial fulfillment of the requirements for the degree of doctor of philosophy. 

Author's acknowledgments. The author wishes to acknowledge his indebtedness to Professor W. H. 
Chandler for the direction of this work and for helpful criticisms given during its progress. 

613 



614 ' D. B. Carrick 

nursery were almost completely destroyed. In the orchard, apple trees 
from three to fifteen years old, situated on a north slope on light soils and 
unprotected by snow or vegetation, suffered very severely. It was noted, 
however, that hardy varieties rooted from the scion often withstood the 
same cold that killed trees which were wholly on seedling roots. The 
varieties least injured were: first, Siberian crab apple; second, native 
crab apples and the Hibernal type of Russian apples; and third, varieties 
of western origin such as Northwestern. 

The most resistant plum stock seemed to be Prunus Besseyi. No 
injury in any case was found in this species. Prunus americana was the 
next in resistance, being only slightly injured. Marianna roots were 
seriously damaged, while Peach and Myrobalan roots were entirely 
killed. 

The hardiest cherry root observed was the Morello stock, which, except 
where exposed, escaped with slight injury. Trees in the nursery on 
Mazzard stock were practically a total loss, while those on the Mahaleb 
stock suffered less. 

From the foregoing observations Craig concluded that the absence of 
snow or other protective covering during an unusually severe winter 
accounted for the very considerable root injury. To prevent a recurrence 
he advocated the use of desirable cover crops, the employment of the 
hardiest stocks available, and the deep planting of young trees, especially 
on the loess soils of the State. 

Emerson (1903) conducted an interesting experiment to determine the 
influence of mulching and soil moisture on the freezing of roots. He 
filled seven boxes, 2 feet square and 18 inches deep, with a loam soil, and 
planted twenty-five apple seedlings in each box. 

In the box protected by a 4-inch straw mulch, there was a soil moisture 
content of 16 per cent. By this treatment no roots were found dead and 
but seven were injured. In the box covered occasionally with snow and 
containing 15.8 per cent of moisture, seven roots were dead and eight 
were injured. In the unprotected boxes the injury seemed to vary inversely 
with the increased water content of the soil. With 10.4 per cent of moisture 
the roots of twenty trees were dead and five were uninjured; with 25.6 per 
cent of moisture, eight roots were dead, four were injured, and thirteen 
were uninjured. Not a root was injured in a box stored in a cool, dry 
place, altho its soil contained only 10 per cent of moisture. 



Resistance of Roots of Fruit Species to Low Temperature 615 

Emerson (1906) found some striking differences in the protection of 
certain cover crops against deep freezing. In one case in which the snow 
was held, the ground froze to a depth of six inches where corn was planted, 
twelve inches with a heavy cover of oats, fifteen inches under a medium 
heavy crop of millet, and twenty-four inches where the soil was bare. 
These facts suggest the use of cover crops which will catch and hold the 
snow in regions where root injury is prevalent. 

Macoun (1908) mentions the killing of roots as one of the ten forms of 
winter injury occurring in Canada. He recommends the use of cover crops 
as a means of increasing the soil moisture and holding the snow. His 
observations on the effect of soil moisture were similar to the expe- 
rience of Emerson. He states also that the grafting of apples on the 
garden crab-apple trees has somewhat reduced the root injuries due to 
freezing. 

By means of careful artificial freezings, Chandler (1913) obtained a 
considerable amount of interesting data on the relative hardiness of 
various fruit stocks. He found that the range of killing temperature of 
apple, peach, pear, and plum roots was from -3 C. in summer to -12° 
in late winter with rather rapid freezing. He compared the killing tempera- 
ture of apple roots actively growing in the greenhouse with that of dormant 
ones in cold storage, in basement storage, and outside in frozen soil, 
respectively. The three dormant treatments showed little difference in 
resistance, but the active tissues killed at three centigrade degrees higher 
than did the dormant roots. Similar comparisons of peach and Marianna 
plum roots showed somewhat less variation between the conditions of 
growth and dormancy. 

Chandler observed also a diminished hardiness in the roots farthest 
from the crown, apparently varying with their soil depth. He demon- 
strated further that in most cases the roots coming from the scions of 
Ben Davis apple trees were hardier than similar roots from French apple 
seedlings. An extended laboratory determination of the comparative 
resistance of Marianna and Myrobalan plum roots and Mahaleb and 
Mazzard cherry stocks strongly confirmed Craig's observations under 
orchard conditions. 

Mix (1916), while studying sun-scald in the northern part of the Cham- 
plain Valley, New York, observed a great amount of winter injury in the 
roots of apple trees from one to twenty years old. The injured condition 



616 D. B. Carrick 

seemed most serious where fall plowing was practiced and where the trees 
were on light soils and in windy situations. The Ben Davis trees were 
especially susceptible, from 50 to 75 per cent of these being left in a dying 
condition. Northern Spy and Wealthy trees also were injured, but in 
a degree much less than the Ben Davis. Mix observed also some cases 
in which, as he states, " the hardiness of the stock seems to have been 
influenced by the scion." 

METHOD USED IN FREEZING THE ROOTS 

The apparatus used in this study for freezing the roots consisted of: 
an inner chamber of galvanized iron 9 inches long, 1| inches wide, and 30 
inches deep; an outer chamber of the same material, 6 inches long, 
12 inches wide, and of the same depth as the inner chamber; and around 
the outer chamber, 5 inches of insulation held in place by a casing of wood. 
The roots to be frozen were placed in the inner compartment, and were 
surrounded by the freezing mixture of ice and common salt in the second 
chamber. At no time was the actual tissue temperature determined, 
but the temperature of the air around the tissues was measured by means 
of three electrical resistance thermometers and a balance indicator. The 
latter instrument consisted of the circuit of a Wheatstone bridge mounted 
in a suitable case with a galvanometer and means for balancing the bridge 
by moving a contact along a slide wire.^ The three electrical resistance 
bulbs, each with leads 5 feet long, were used until the variation in temper- 
ature in the lower part of the freezing chamber was determined. These 
bulbs were standardized by the makers and were carefully checked against 
one another in the laboratory here. The bulbs were securely attached to 
a piece of hardware cloth 6 inches square. The various roots to be tested 
were fastened to this wire by means of rubber bands. The bulbs always 
stood perpendicular to the bottom of the chamber, and the roots were 
always arranged on the cloth parallel to the bulbs. 

Careful tests showed that, while the temperature was uniform at given 
levels within certain limits, it varied slightly at different levels. Because 
of this fact, a complete record as to the injury in the lower and in the upper 
ends of the roots was kept. To further standardize this variation, all 
of the pieces of material used were cut 4 inches in length. When the 

' This is a standard apparatus obtaiaablo from tbo Loeds, Morthrup Company, of Pbtladelphia> 



Resistance of Roots of Fruit Species to Low Temperature 617 

hardware cloth and the bulbs were in position, the roots e?ctended to within 
one inch of the bottom of the chamber in a regular row. 

The difference in temperature on either side of a bulb — that is, hori- 
zontally — within a compass of five inches was found to be negligible. 
However, a number of tests of the temperature in either extreme end of 
the freezing chamber showed that a maximum difference of one centigrade 
degree might exist. Accordingly, no roots were tested at these points. 

In order to subject all the material to as nearly uniform conditions of 
freezing as were possible, the killing temperature of a number of different 
roots was determined at the same time rather than an attempt being made 
to freeze at once many roots of a single sort. Owing to the variety of 
roots used, however, it was neither practicable nor desirable to test all of 
these at any one time. As they naturally divided themselves into groups of 
more or less tenderness, material of similar resistance was usually frozen 
together. 

While the temperature was being gradually lowered, the inner compart- 
ment was kept tightly closed. In no case were any of the roots removed 
before the minimum degree was reached. 

Since several workers have found a distinct influence in the amount of 
injury resulting from the rapidity of cooling, care was taken to allow a 
standard rate of fall for all freezings, except as noted to the contrary. 
This uniform lowering of temperature began at 1.5° C, and reached 
0° in fifteen minutes. The fall from .this point to the desired degree 
was at the rate of one degree ever}^ twenty-two and one-half minutes. 
The minimum temperature was always maintained for fifteen minutes. 
Ordinarily the roots were removed from the chamber and allowed to thaw 
rapidly. 

Russell (1914) and others have noted that the death of a plant from 
freezing is rarely immediate but may be delayed for several days. Because 
of this possibility the treated roots were set aside and examined at different 
intervals. During this time they were kept moist by placing them on a 
hardware cloth which projected above the surface of the water in an agate 
pan. The roots and the pan were covered with a bell jar. 

An inspection of the roots for injury was usually made within from one 
to three days after exposure. In most cases when injury occurred, it 
was apparent by the end of this period. At first microtome sections were 
prepared and the character of the injury was determined with a low- 



618 D. B. Carrick 

power microscope. This was soon found to be unnecessary, since the 
color changes of the frozen cells, except in the gooseberry and the currant, 
were rather striking. The affected tissues of the apple became of some 
shade of brown and appeared water-soaked ; in Mazzard cherry, Myrobalan 
plum, and red raspberry roots, the injured cells were somewhat yellowish; 
while in the blackberry and the dewberry they often appeared almost 
black. The early appearance of Rhizopus species and probably other 
saprophytic fungi on the dead part was also characteristic of injury. 
In not an instance did the fungus or the discoloration appear in the unfrozen 
roots left similarly located for comparison. 

The roots of all species tested from October 24 to November 18 were 
collected from the nursery row. All the leaves were present on the plants 
used in the first determinations and some had not fallen in the latter 
freezings. The remainder of the material was kept in common storage 
and removed as needed. With this material the temperature varied 
somewhat, due to outside changes, but it seldom went below 0° C. and did 
not rise above 5° until April 1. The plants were stored in normally 
moist sawdust, and there was little opportunity for them to dry out later 
as they were placed on the hardware cloth attached to the resistance 
bulb while in storage and were then immediately frozen. 

RESULTS OF THE EXPERIMENTS 
RESISTANCE OF APPLE ROOTS TO LOW TEMPERATURE 

For all the tests conducted, the diameter of each end and of the center 
of the root, and the date of freezing, are recorded as possible factors that 
might influence the kind or the amount of injury. The results of the 
tests with apple roots are shown in table 1. 

Four kinds of seedlings were used: one-year American stocks, grown 
in this country but from French seed; one-year French seedHngs imported 
from France; two-year French roots which had grown for one year in the 
nursery here; and one-year stored French seedlings which had been held 
at approximately 0° C. in cold storage for one year. 

One noticeable feature in the apple freezings was the differences in the 
individual resistance of roots similarly treated and frozen apparently 
under the same conditions. Unless the temperature is above or below 
the average freezing point, all gradations of injury may occur. 



Resistance of Roots of Fruit Species to Low Temperature 619 
TABLE 1. Effect" of Low Temperature on Roots of Apple Seedlings 



Temper- 
ature 
(centi- 
grade) 


Date of 
freezing 


Variety 


Diam- 
eter 
of roots 

(milli- 
meters) 


Num- 
ber of 
roots 


Num= 
ber of 
roots 
unin= 
jured 


Per cent of cells killed 
in injured roots 


Cam- 
bium 


Phloem 


Cortex 


~-T 


October 24 

to 

November 18 


American 


7x6 
5x4 
4x3 


2 
4 

7 


2 
3 












50 
40 


50 
40 


50 
40 




2-year 
French 


7x5 
5x4 
4x3 


10 

s 

6 


10 

5 










40 
60 


40 
50 


40 
50 


—8° 


American 


5x4 
4x3 
3x3 


1 
S 
1 


1 

2 










40 

50 


20 
50 


20 
50 




2-year 
French 


7x5 
5x4 
4x3 


3 

2 

13 


3 

2 
2 


















60 


60 


60 


—9° 


American 


7x5 
6x5 
5x4 


3 

2 
4 


1 

i 


35 
25 
90 


35 
25 
90 


35 
50 
90 




2-year 
French 


7x5 
5x4 
4x3 


2 
6 
5 


2 
5 










75 


75 


75 










—9° 


December 

to 

January 


American 


9x7 
6x6 
5x4 


5 

4 
4 


2 
1 


80 
50 

75 


35 
45 
60 


35 
45 
60 




2-year 
French 


7x5 
5x3 
4x2 


6 
6 
6 


4 

2 
3 


5 
35 

80 


5 
20 
65 


10 
20 
65 


—10° 


2-year 
French 


7x5 
5x3 
4x3 


5 
14 
11 


3 
1 


45 
50 
60 


15 
50 
60 


15 
50 
60 


—12° 


2-year 
French 


8x6 
4x3 


2 
3 




5 
100 


5 
100 


5 
100 


—9° 


February 
to March 


American 


7x6 
5x4 


9 
9 


6 
4 


20 
60 


10 
60 


10 
60 




2-year 
French 


8x5 
3x2 


3 
3 


3 










50 


50 


50 



620 



D. B. Carrick 

TABLE 1 (continued) 



Temper- 
ature 
(centi- 
grade) 


Date of 
freezing 


Variety 


Diam- 
eter 
of roots 

(milli- 
meters) 


Num- 
ber of 
roots 


Num= 
ber of 
roots 
unin= 
jured 


Per cent of cells killed 
in injured roots 


Cam- 
bium 


Phloem 


Cortex 


—10° 


February 

to 

March 

(continued) 


American 


7x6 
5x4 
3x2 


12 

8 

10 


10 


65 
50 
55 


10 
50 
55 


""45 
50 




2-year 
French 


7x5 
3x2 


3 

8 


3 

1 










65 


65 


65 


—11° 


American 


7x6 
5x4 
3x2 


12 

6 

30 


4 

2 
20 


60 
55 

40 


30 
55 
40 


25 
55 
40 




2-year 
French 


6x5 
3x2 


5 

20 


5 
II 










45 


45 


45 




1-year 
French 


8x5 
3x2 


5 

8 












2 


40 


10 


30 


—12° 


American 


7x6 
5x5 
4x3 
3x2 


9 
11 

8 
22 


1 


80 
85 
75 
80 


70 
85 
75 
80 


70 

85 
75 
80 




2-year 
French 


6x5 
3x2 


5 
33 




75 
85 


75 

85 


75 

85 




1-year 
French 


8x6 
3x2 


4 
19 


4 

5 












15 


15 




1-year 
French, 
stored 


8x5 
3x2 


4 
22 


7' 


100 
55 


100 
55 


80 
55 


—12.5° 


1-year 
French 


8x6 


4 


1 


50 


50 


50 


—13° 


American 


7x6 
3x2 


8 
16 


2" 


90 

75 


90 
75 


90 
75 




1-year 
French, 
stored 


3x2 


9 




85 


85 


85 


—14.5° 


American 


7x6 
3x2 


15 

27 




80 
90 


80 
90 


80 
90 



Eesistance of Roots of Fruit Species to Low Temperature 621 

TABLE 1 (continued) 



Temper- 
ature 
(centi- 
grade) 


Date of 
freezing 


Variety 


Diam- 
eter 
of roots 

(miUi- 
meters) 


Num- 
ber of 
roots 


Num=" 
ber of 
roots 
unin= 
jured 


Per cent of cells killed 
in injured roots 


Cam- 
bium 


Phloem 


Cortex 


—14.5° 

(cone.) 


February 

to 

March 

(concluded) 


1-year 
French 


8x7 
3x2 


2 
6 


1 


100 
100 


100 
100 


75 
100 


—9° 


March 29 

to 
April 15 


1-year 
French 


8x6 
6x4 


2 
3 


1 
3 




60 














American 


8x6 
6x4 


8 
4 


8 

2 










25 














1-year 
French, 
stored 


8x6 


3 




100 


100 


100 


—10° 


1-year 
French 


8x6 
6x4 
5x3 


4 
4 
4 












3 


100 
60 


45 
60 


45 

60 




American 


8x6 


5 


5 


















1-year 
French, 
stored 


8x6 


5 


1 


100 


100 


100 


—11° 


1-year 
French 


8x6 
3x2 


2 
6 


2 










100 


100 


100 




American 


8x6 
6x5 


5 
4 


1 


75 
100 








100 


100 




1-year 
French, 
stored 


8x6 


2 




100 


100 


100 


—12° 


1-year 
French 


8x6 
3x2 


3 
12 


2 


100 
100 


100 
100 


50 
100 




American 


7x5 


8 




100 


100 


100 




1-year 
French, 
stored 


8x6 


3 




100 


100 


100 



622 



D. B. Carrick 

TABLE 1 (concluded) 



Temper- 
ature 
(centi- 
grade) 


Date of 
freezing 


Variety 


Diam- 
eter 
of roots 

(milli- 
meters) 


Num- 
ber of 
roots 


Nuni= 
ber of 
roots 
unin= 
jured 


Per cent of cells killed 
in injured roots 


Cam- 
bium 


Phloem 


Cortex 


—7° 


April 16 

to 
May 8 


1-year 
French 


8x6 
3x2 


2 
5 


2 










50 


50 


50 




American 


8x6 
6x4 


7 
4 


1 


100 


100 


90 














1-year 
French, 
stored 


7x5 
3x2 


2 
4 


2 
4 
























—8° 


1-year 
French, 
stored 


7x6 
3x2 


4 
13 


4 
4 










80 


25 


25 




American 


8x6 
6x4 


4 
5 


I 


80 
90 


25 
80 


25 

80 




1-year 
French, 
stored 


8x6 
6x5 


2 
2 




10 
90 








90 


90 


—9° 


1-year 
French 


8x6 
3x2 


2 

7 


2 

7 


























American 


8x6 


6 


3 


25 














1-year 
French, 
stored 


7x4 
3x2 


2 
4 


2 










100 


100 


100 


—10° 


American 


8x6 
6x5 


6 
6 




70 
100 


60 
100 


60 
100 



It is a common opinion among some nurserymen that the French- 
grown apple stocks are hardier than the home-grown seedlings. The 
results obtained from the freezing of hundreds of roots of each stock 
indicate that these differences in resistance are negligible. Both stocks 
are found to show considerable injury from -11° to -11.5° C, and at 
-J 2° few of either sort survived. The two-year French roots were grown 



Resistance of Roots of Fruit Species to Low Temperature 623 

under unfavorable conditions in the nursery, and apparently because of 
this were more easily killed than the one-year stock. The one-year 
seedlings held in cold storage for one year showed about the same hardiness 
as the two-year roots. 

The observations of Chandler (1913) led him to conclude that the 
hardiness of the root tissues varies with the season. This is to be expected 
and the results obtained readily support this theory. The material frozen 
in October and November shows a marked tenderness compared with 
roots tested in February and March. The period of maximum resistance 
seems to end somewhat before the last of March, tho the date would, of 
course, vary with the conditions affecting after-ripening and possibly 
also with the variety. From the first of April until these observations 
ceased, an increasing amount of injury was noted. This range of hardiness 
indicates a difference in resistance of between three and four centigrade 
degrees. These seasonal differences obtain, not only in the apple seedlings, 
but in all the roots reported in this paper. 

The influence of the size of the root in withstanding cold seems reasonably 
well established by the data in table 1 as well as by those in the succeeding 
tables. The resistance is in direct proportion to the diameter of the root. 
In practically all cases in which the whole forked roots of the French 
seedling were employed, the small roots killed first. Similarly, the smaller 
roots of the American stocks having the same soil depth suffered more 
quickly and severely than the larger roots. 

The results in the apple tests seem to point rather clearly to the relative 
resistance of the different tissues in these roots. It is seen, in practically 
all instances in which injury occurs, that the cambium is the first tissue to 
be killed. This is followed closely by the phloem, while the cortex seems 
somewhat hardier than either of the other tissues. Only a few cases are 
recorded in which the cortex alone was severely injured, tho frequently 
the three tissues were equally affected. Unless the temperature is especially 
low for apple roots, or they are especially tender as in the fall and the spring, 
the cambium, the phloem, and the cortex are browned without further 
injury. Occasionally under extreme conditions the xylem and the pith 
may be killed, in which case they both seem to show about equal resistance. 
An exposure at -20° C. would ordinarily kill all the cells in the roots of 
any apple seedlings tested in these experiments, even when they were in 
a dormant condition. 



624 D. B. Carrick 

A number of observations were made on material four inches long, 
in which two inches of the plant represented the stem above the soil level 
and two inches represented the root below the surface of the ground. 
From the results of these freezings some indications were given as to just 
where the tenderness of the root tissues ended and the well-known hardiness 
of the stem tissues began. Where injury occurred to the specimen, the 
region of browning much oftener than otherwise extended from the lower 
end of the root upward, decreasing abruptly at the crown. This is some- 
where near the point of differentiation of root and stem structures. It was 
indicated from these data that this difference in resistance may have been 
brought about by a change in cellular structure. 

While Chandler (1913) seemed to find that roots deeper down in the 
soil were tenderer than those near the surface, an examination of his 
data shows that the deeper roots were also considerably the smaller in 
diameter. Many observations of roots of equal transverse section and 
growing at different soil levels were recorded from time to time. From 
the results of these observations, it was suggested that the size of the root 
was, perhaps, a greater factor in its resistance than the soil depth at 
which it grew. 

From the foregoing considerations it is rather difficult to assign a fixed 
temperature at which an apple-seedling root may be partially or completely 
injured b}^ freezing. Examination of all of the material tested showed that, 
while severe injury is found at exposures ranging from -7° to -13° C, 
one French root survived a temperature of -14.5°. However, the 
majority of the dormant roots were seriously injured in the three outer 
tissues by a temperature of -12° C. 

RESISTANCE OF PEAR ROOTS TO LOW TEMPERATURE 

In the work with pear roots the comparative tenderness of two-year 
French stock (Pijrus communis) and one-year Kieffer stock was determined. 
The two-year roots were given the same field treatment the second year 
as was given to the two-year French apples previously mentioned. A 
few one-year French stocks were also available in 1916. 

In almost all cases, as shown by the data recorded in table 2, the one- 
year Kieffer roots proved more resistant than either of the French stocks. 
At an exposure of -10° C. in the January-March period, the Kieffer roots 
show a less number and percentage affected than do the two-year French 



Resistance of Roots of Fruit Species to Low Temperature 625 

roots. The temperature of -11° during dormancy was too low for the 
survival of either species. In the April tests at -8° the Kieffer stock 
again demonstrates its superiority. When exposed to -9° in April the 
Kieffer shows only a small amount of injury in the phloem while the 
two-year French roots were killed thruout. 

TABLE 2. Effect of Low Temperature on Roots of Pear Seedlings 



Temper- 
ature 
(centi- 
grade) 


Date of 
freezing 


"Variety 


Diam- 
eter 
of roots 

(milli- 
meters) 


Num- 
ber of 
roots 


Num- 
ber of 
roots 
unin= 
jured 


Per cent of cells killed 
in injured roots 


Cam- 
bium 


Phloem 


Cortex 


— 7° 


October 24 

to 
December 15 


2-year 
French 


7x6 
4x3 


8 
5 


6 


20 
100 








100 


100 


—8° 


8x6 
5x3 


10 

5 


2 


75 
100 


75 
100 


75 
100 


—9° 


7x5 
5x3 


3 
6 


1 


50 
100 


50 
100 


50 
100 


—10° 


9x8 
4x3 


3 
6 




60 
100 


60 
100 


60 
100 


—9° 


January 

to 
March 


2-year 
French 


8x6 
5x3 


5 

8 


4 


100 
100 


100 
100 


100 

100 


—10° 


9x7 
5x4 


4 
13 


1 


100 
100 


100 
100 


100 
100 




1-year 
Kieffer 


6x6 


6 


3 


60 


40 


40 


—11° 


2-year 
French 


9x7 
6x4 


5 

7 


1 


'80 

85 


85 
80 


85 
80 




1-year 
Kieffer 


7x6 


7 




100 


100 


100 


—12° 


2-year 
French 


7x6 


4 




100 


100 


100 




1-year 
Kieffer 


8x7 
7x6 


2 
2 




100 
10 


100 
45 


100 
45 


—7° 


April 
1 to21 


2-year 
French 


8x6 
4x3 


2 
4 


2 
3 










50 


50 


5C 



626 



D. B. Carrick 
TABLE 2 (concluded) 



Temper- 
ature 
(centi- 
grade) 


Date of 
freezing 


Variety 


Diam- 
eter 
of roots 

(milli- 
meters) 


Num- 
ber of 
roots 


Num= 
ber of 
roots 
un!n= 
jured 


Per cent of cells killed 
in injured roots 


Cam- 
bium 


Phloem 


Cortex 


—7° 


April 
1 to 21 

(concluded) 


1-year 
Kieffer 


6x6 
6x3 


3 
3 


3 








(cone.) 


25 




100 


—8° 


2-year 
French 


8x5 


3 




100 


100 


100 




1-year 
Kieffer 


6x6 


9 


7 


100 


100 


100 




1-year 
French 


6x6 
5x4 
4x3 


2 
12 

8 


2 
4 










60 
70 


60 
70 


60 
70 


—9° 


2-year 
French 


7x5 


3 




100 


100 


100 




1-year 
Kieffer 


7x5 


3 







15 







1-year 
French 


6x4 
3x2 


9 

7 




75 
100 


75 
100 


75 
100 


—10° 


2-year 
French 


10x6 


3 




100 


100 


100 




1-year 
Kieffer 


7x6 


3 




100 


100 


100 




1-year 
French 


8x5 


3 




100 


100 


100 



The pear roots, like those of the apple, showed individual variations — 
an increase in hardiness with an increase in diameter, a region at the crown 
less tender than the root below, little influence due to depth below the 
soil surface, relative tenderness of the same tissues, and a gradual acquiring 
of hardiness thru the winter, reaching the maximum in February and 
March. This seasonal hardiness, however, seems rather more delayed 
in the pear root than in the apple. 



Resistance of Roots op Fruit Species to Low Temperature 627 

If the resistance of the pear and the apple seedlings is contrasted, it is 
found that an approximate difference of from one to two degrees generally 
obtains, and sometimes even a much greater difference. Thus, while 
in March the apple does not begin to show much injury until a temperature 
of -11° or -12° C. is reached, -10° or -11° is sufficient to kill most of the 
tissues, except the xylem and the pith, in both the French and the 
Kieffer pear stocks, 

resistance of elberta peach roots to low temperature 

The name Elberta as used here refers only to the bearing surface of the 
tree and has no reference to the origin of the roots. The peach stocks 
probably were derived from several different varieties; at least, the range 
of variation presented in table 3 indicates such a possibility. 

TABLE 3. Effect of Low Temperature on Roots of Elberta Peach Trees 



Temper- 
ature 


Date of 
freezing 


Diam- 
eter 
of roots 

(milli- 
meters) 


Num- 
ber of 
roots 


Num= 
ber of 
roots 
unin= 
jured 


Per cent of cells killed ia 
injured roots 


(centi- 
grade) 


Cam- 
bium 


Phloem 


Cortex 


Pith 


—8.5° 


February 12 

to 

March 24 


12x6 
5x4 


2 
4 


2 
















15 














—10° 


15x8 

10x6 

7x5 

5x4 


3 
6 
5 

7 


2 


100 
90 

100 
65 


100 
90 

100 
65 


100 
90 

100 
65 


100 
60 
55 
45 


—11° 


15x8 

10x9 

7x5 

5x4 


1 
5 

4 

7 


2 


100 
30 


100 
30 


100 
35 


'45 
100 




35 


35 


35 


100 


—12° 


12x8 

10x6 

7x5 

4x3 


5 
5 
3 
4 




60 
40 


60 
40 


60 
40 
40 
50 


100 
100 
100 






50 


50 


100 


—14.5° 


7x6 
7x5 


5 
5 


1 

1 


65 
25 


65 
25 


65 
35 


100 
100 



028 



D. B. Carrick 

TABLE 3 {concluded) 



Temper- 
ature 


Date of 
freezing 


Diam- 
eter 
of roots 
(milli- 
meters) 


Num- 
ber of 
roots 


Num= 
ber of 
roots 
unin= 
jured 


Per cent of cells killed in 
injured roots 


(centi- 
grade) 


Cam- 
bium 


Phloem 


Cortex 


Pith 


—5.5° 


March 25 

to 
April 25 


7x5 


7 


3 




25 


25 




—7° 


11x10 
7x5 


3 
6 


2 
2 


20 


100 
20 


100 
20 




—8° 


12x6 
7x5 
5x4 


2 
2 
4 






10 

60 

100 


25 

60 

100 






1 


"lOO 


100 


—9° 


10x6 


3 




100 




100 




—10° 


11x10 


3 




100 


100 


100 


80 


—11° 


7x5 


3 




100 


100 


100 


75 



During the middle of February an exposure at -10° C, included in the 
February-March period, shows an average injury of 75 per cent in all 
tissues except the xylem in nineteen out of twenty-one roots. The tests 
at -11°, which were made on March 1, indicate an average injury of less 
than 50 per cent. An average injury of from 55 to 60 per cent in all the 
cells is seen at a temperature of - 12°, altho at two and one-half degrees 
lower two roots out of ten were uninjured. 

As a general rule the order of resistance of the various tissues in the 
peach root seems to be as follows: pith, cortex, phloem, cambium, xylem. 
At -18° C. or below, the xylem was usually killed during the hardiest 
period. In most cases during February and March the pith is the tissue 
most easily killed, but in April the cambium is the least resistant. 

It is not so easy, with the data at hand, to assign an arbitrary limit 
within which the peach root is injured by freezing. This is because of 
the great variation in the root tissues. The peach cambium certainly is 
as hardy as the pear cambium, tho less so than the apple. Regardless of 
the size of the root, most of the peach material tested showed some injury 



Resistance of Roots of Fruit Species to Low Temperature 629 

at -10° C, and, except in unusual cases, serious injury occurred at -11°. 
This would then place the hardiness of the peach root very close to that of 
either pear seedling. 

COMPARATIVE RESISTANCE OF MAZZARD AND MAHALEB CHERRY ROOTS TO 

LOW TEMPERATURE 

In the cherry freezing determinations previous to January, 1916, only 
two-year cherry seedlings were used. Subsequent to that date, only 
one-year material was tested. A few roots of Prunus Besseyi were avail- 
able in March. 



TABLE 4. Effect of Low Temperature on Mazzard and Mahaleb Cherry Root? 



Temper- 
ature 


Date of 
freezing 


Variety 


Diam- 
eter 
of roots 

(milli- 
meters) 


Num- 
ber of 
roots 


Num- 
ber of 
roots 
unin- 
jured 


Per cent of cells killed in injured 
roots 


(centi- 
grade) 


Cam- 
bium 


Phloem 


Cortex 


Pith 


Xylem 


7° 


October 24 

to 

December 11 


Mahaleb 


7x3 
5x4 


5 
5 


5 
4 














25 






















Mazzard 


8x3 
7x5 


2 
2 




50 
50 


50 
50 


50 

50 


















8° 


Mahaleb 


10x8 
9x7 
5x4 
4x2 


3 
5 
5 


2 

1 
3 














25 
15 
50 


25 


25 














60 


60 














Mazzard 


9x5 
5x3 


1 
4 


1 














80 


80 


80 












, ..9» 


Mahaleb 


b X 5 
5x3 


10 
2 


4 
1 


50 
50 
































Mazzard 


6x5 


4 




80 


80 


80 












—10° 


Mahaleb 


10x5 
5x2 


2 
2 


1 




. . 50 








100 


100 


100 












12° 


Mahaleb 


15 X 13 


2 




100 


100 


100 












9° 


January 1 

to 
March 29 


Mahaleb 


7x5 


2 


2 


























Mazzard 


6x6 
5x4 


2 
3 


2 














45 


45 


45 












' ■ 10° 


Mahaleb 


6x2 


2 


2 


























Mazzard 


7x6 
4x2 


2 
2 




30 


30 


30 


























11° 


Mahaleb 


7x5 
4x2 


6 
2 


6 














50 


50 


50 














Mazzard 


8x8 
5x4 


6 
4 






85 
100 


85 
100 


85 
100 




















650 



D. B. Carrick 



TABLE 4 (concluded) 



Temper- 
ature 
(centi- 
grade) 


Date of 
freezing 


Variety 


Diam- 
eter 
of roots 

(milli- 
meters) 


Num- 
ber of 
roots 


Num- 
ber of 
roots 
unin- 
jured 


Per cent of cells killed in injured 
roots 


Cam- 
bium 


Phloem 


Cortex 


Pith 


X lem 


—11° 


January 1 

to 
March 29 
(.concluded) 


Prunus 
Besseyi 


9x7 
6x3 


2 
4 




100 
100 


100 
100 


100 
100 






'cone.) 












—12° 


Mahaleb 


7x6 
6x3 


3 
2 


2 


10 
100 


10 
100 


10 
100 




















Mazzard 


7x6 


4 




100 


100 


100 














Prunus 
Besseyi 


7x8 
7x6 


2 
2 




50 
100 




25 
30 








100 




—15° 


Mahaleb 


10x8 
7x6 


7 
2 


i' 


20 
30 


20 
30 


20 
30 




















Mazzard 


10x8 


7 




100 


100 


100 














Prunus 
Besseyi 


7x7 


2 




100 


100 


100 













—17° 


Mahaleb 


8x7 


2 




75 


75 


75 












Mazzard 


8x7 


2 




100 


100 


100 


100 






Prunus 
Besseyi 


9x7 


4 




100 


100 


100 


100 


50 


—7° 


March 30 

to 
April 20 


Mahaleb 


9x4 


2 


2 


























Mazzard 


9x8 


4 




100 


100 


100 












—8° 


Mahaleb 


8x5 


4 


4 


























Mazzard 


12 X 11 

8x6 


2 
2 


1 


40 
100 


40 
100 


40 
100 


















—9° 


Mahaleb 


9x5 
8x3 


2 

5 


2 
4 














15 


15 


15 














Mazzard 


10x8 
8x5 


5 
5 




100 
100 


100 
100 


100 
100 


















—10° 


Mahaleb 


7x6 
5x2 


5 
2 


5 














40 


40 


40 














Mazzard 


10x9 

8x8 


4 
4 




100 
100 


100 
100 


100 
100 








100 


50 


—11° 


Mahaleb 


8x4 


2 


2 


























Mazzard 


8x8 


3 




100 


100 


100 


100 




—12° 


Mahaleb 


9x6 

7x4 


2 
3 




60 
5 


75 


75 
10 




















Mazzard 


12x10 
8x7 
7x4 


2 
4 
3 




100 
100 
100 


100 
100 
100 


100 
100 
100 


100 
100 
100 


" ioo 

100 



Resistance of Roots of Fruit Species to Low Temperature 631 

The most striking fact brought out by the data in table 4 is the uniform 
tenderness of the Mazzard as compared with the Mahaleb stock. This 
difference can readily be seen in any comparable instance. It extends 
thru all stages of maturity. Thus, during November, Mazzard tissue 
was injured much more severely when exposed to -S° C. than was cor- 
responding Mahaleb stock tested at -9°. In the January-March period 
a similar difference is noted; the six larger Mazzard stocks given an exposure 
at -11° show 85 per cent browning in the three outer tissues, while three 
smaller Mahaleb roots were similarly affected only 10 per cent when 
exposed at -12°. At -15° the Mahaleb tissue suffers relatively little 
injury, but the two roots subjected to -17° are mostly killed. In the 
March-April period the continued resistance of the Mahaleb tissue is 
striking. On April 15 it is about three or four degrees hardier than the 
Mazzard, which when exposed to -10° is seriously injured in the pith 
and the xylem. These results are in accord with the field observations 
of Craig (1900) and the laboratory studies of Chandler (1913). 

The freezing tests with Prunus Besseiji, altho this is a plum species, 
are included in the cherry data since it is frequently used as a cherry stock. 
These results with Prunus Besseyi do not bear out the experience of most 
writers regarding its exceptional hardiness. During the January-March 
exposures, it is noted that at -11° C. this variety was injured somewhat 
■more than was the Mazzard. At -12° it was rather more resistant than 
the Mazzard but the pith in the smaller roots was killed thruout. At 
-15° and -17° it suffered equally with the Mazzard or worse. 

Under field conditions with severe freezing, Craig (1900) found Prunus 
Besseyi much hardier than all other stocks used for cherries. The writer 
is not prepared to say that the hardiness of this species has been over- 
estimated. His own very limited experience, however, shows it to be 
inferior in resistance to Mahaleb, and slightly better than Mazzard. 
Since the writer is not familiar with the Prunus Besseyi stock, it is of course 
possible that the roots tested as recorded above were not of this species. 
The only evidence that they were correctly named is from the nurseryman 
who sold them as such. 

A small amount of data on Prunus avium and Prunus pennsylvanicum, 
not included in table 4, indicate merely that these roots seem to be quite 
as easily killed by freezing as are Mazzard roots. Since these roots were 
taken directly from the partly frozen ground in April, they were rather 



632 D. B. Carrick 

moist and were probably beginning activity. A larger number of deter- 
minations under different conditions might entirely change the tendency 
just mentioned. 

Considering the data on the four cherry stocks, their order of relative 
hardiness seems about as follows: Mahaleb, Prunus Besseyi, Prunus 
pennsylvanicum, Mazzard. If the Mahaleb cherry is compared with 
the apple, it is seen that the resistance of the former is markedly superior 
in most cases. In large Mahaleb roots during their hardiest period, 
little injury is found under -14° C, while at -15° the injury is relatively 
small. Prunus Besseyi did not survive a temperature of -11°. Prunus 
pennsylvanicum succumbed at -10° or -11°, altho the date of freezing 
may partly account for its tenderness. The Mazzard roots in no instance 
withstood -11°, but the number of tests run at -10° was insufficient 
to place this as its minimum. From these results the Mazzard cherry 
stock does not appear hardier than Kieffer pear stock. 

RESISTANCE OF MYROBALAN PLUM ROOTS TO LOW TEMPERATURE 

Unfortunately, only one commonly used plum stock was available in 
this work, aside from the Prunus Besseyi roots included in table 4 with 
the cherry stocks. The number of one-year Myrobalan roots tested was 
too small to give very conclusive results. However, some indication 
at least of its comparative hardiness may be gained from table 5. The data 
in this table place the one-year Myrobalan root in the same group in regard 
to hardiness as the pear and the Mazzard cherry. The Myrobalan plum 
does not appear quite so hardy as the Kieffer pear and probably it would 
prove to be less hardy than a vigorous one-year French pear. The fact 
that the roots of the latter are normally somewhat larger than the 
average plum roots, would give still more evidence in favor of the 
superior hardiness of the pear. 



Resistance of Roots of Fruit Species to Low Temperature 633 

TABLE 5. Effect of Low Temperature on Mtrobalan Plum Roots 



Temper- 
ature 


Date of 
freezing 


Diam- 
eter 
of roots 
(milli- 
meters) 


Num- 
ber of 
roots 


Number 

of roots 

uninjured 


Per cent of cells killed 
in injured roots 


(centi- 
grade) 


Cam- 
bium 


Phloem 


Cortex 


, yo 


October 24 

to 
December 20 


8x7 
5x3 


2 
5 




50 
65 


50 
65 


10 






65 


—8° 


5x4 


3 




100 


100 


100 


—9° 


7x5 
5x3 


3 
2 


1 


100 
100 


100 
100 


100 
100 


—10° 


9x5 

8x7 


2 
2 




80 
65 


80 
65 


80 
65 


—9° 


January 1 

to 
March 29 


7x6 
5x4 
2x1 


6 
11 
11 




100 
30 
40 


100 
30 
40 


100 
35 
40 


—10° 


8x5 
5x4 


2 
9 




100 
80 


100 

80 


100 

80 


—11° 


9x7 
5x4 


2 
4 




75 
100 


75 
100 


75 
100 


—8° 


April 1 to 8 


6x5 
5x4 
3x2 


5 

7 

13 




80 
25 
80 


80 
25 
80 


80 

60 

100 



resistance of the roots of six grape varieties to low temperature 

It is well known that there is a rather wide difference in hardiness in 
the canes of certain varieties of grapes. Such a variation, tho less impor- 
tant and conspicuous, is found also in grape roots. To determine these 
differences, six varieties were selected for testing, embracing several 
species. 

According to Hedrick (1908), the varieties used represent the following 
species: Concord, Vitislabrusca; Clinton, Vitis vulpina and Vitis labrusca, 
the variety being more characteristic of the former species; Diamond, 
Vitis labrusca and Vitis vinifera, the former predominating; Lindley, 
Vitis labrusca Q>nd Vitis vinifera; 'Norton, Vitis aestivalis and Vitislabrusca, 



<t» 



V B Cjubkum 



i$.>- ^^*f»jijii '»j/0if;rf :ot^}f*^ Ufmt 'ji^j^. t^jmt^ ^^a^i, ^jfti^mamak, 

i ■^ik'A mA V'4}tA. kihwam, "^^ ^mtt^ p fAfimmHi ms, ^ ^ 

wtttm wm^ Mp m MmmUr^ %■ fffnatiiir m tmf knr nmM %m tm e d m * iMgle 
Ummm> ^^ iM» pkmkU #^ mnm. mmmA', ikm^^m m Mwrm^r » m» 

iM^ IJmmmhffjf mt^ Um iimmt' c mtt m nAMk Urn ti mm m mm n t tHrnr 
^r Iwcsamp Cl i mm ^ ^Ufmrn^mA t fu m imi Mm^^m dbrigt mmft; 



TAMM (^. ISfn^ 'h* Um Ttamnummt' «¥ -mm ISm«» m§»Gi 





it^/^ 


1 
>•«*«*' 


mtttfr 




-** 










-'W 


' ,. . 


''.'■ 




-«* 








— *r 






'*3 


-»» 









fl^'lWPB'4^ 48HW JHIVSVlV 



.ry«j« f'./W^***; |^«il 



bM«N» 



3t 






N^ 






ConitMt^ 






>ac«>y- 



<-^ ^-^ !*^i>r-' 










34«&^ 


~ 


-'^t 


t> Hit- 


's. . 


• 


\, -t 




rv 











— «s* 



OUtftMt 



Ms*.- 







^ 


f 


^1 








OMkKMM 
CtkHftW 




> 




V 








t V ■ 


.■J 








.^ 


^ 




^- 




V 




I* 



u 



•<A' 






t I 






Mill miybtil llMt^. btui \ 'ixcika^xi pb»k>f«jis IWwx^vvr, 



636 D. B. Carrick 

ent. Only scattering injury is recorded at -11°, -12°, and -13° C. At an 
exposure of -14.5°, twenty-two out of twenty-seven Concord roots were 
uninjured and only a trace of cambium and cortex injury was noted in the 
remainder. One-half of the Clinton and two-thirds of the Diamond roots 
were injured more than 50 per cent by the same temperature. At -15.5° 
an injury of 20 per cent is seen in one-third of the Concord roots and 15 
per cent more in the other two varieties. At -18°, however, the cambium, 
phloem, and cortex tissues were completely injured in all roots, with some 
xylem injury in the Diamond and the Concord. By March 21 tender- 
ness began to return, and a few days later these varieties were severely 
injured by temperatures several degrees higher. 

A contrast of the root resistance in the varieties of the second class 
shows the following order of hardiness: Norton, Lindley, Cynthiana. 
The variations, however, are so sUght that they may be entirely 
disregarded. 

In 1917 Cynthiana was quite as resistant as Norton, as shown by the 
injury in both at the higher and lower temperatures. Lindley seemed to 
be a trifle easier to kill than either Cynthiana or Norton in 1916, but here 
again the differences are slight. The limits of this second group as shown 
in table 6 lie between -10° and -12° C, the roots usually undergoing 
considerable injury at -11°. In relative hardiness this places these 
varieties between the Mazzard cherry and the apple. 

The Clinton, Concord, and Diamond roots, even excluding the influence 
of size, are considerably more resistant than apple roots, and Concord 
and Clinton seem equal if not superior to the Mahaleb stock. 

The results shown on comparing the hardiness of the respective species 
of grapes are somewhat as would be expected. Vitis aestivalis, represented 
by Norton and Cynthiana, is not adapted to severe cold, and this may 
account for the fact that its range is limited to the South. The tenderness 
of Lindley is probably due in part to the influence of Vitis vinif era, which, 
as is well known, will not survive the winter in the latitude of New York 
State without much protection. Concord and Diamond represent Vitis 
labrusca, the Northern Fox grape, which, while restricted in distribution, 
is found in Maine. Vitis vulpina, represented by Clinton — a variety 
with extremely resistant roots — has the greatest range of any American 
species of grape, it having been found in Canada north of Quebec. 



Resistance of Roots of Fruit Species to Low Temperature 637 

resistance of blackberry, dewberry, and red raspberry roots 

to low temperature 

An attempt was made to test representative varieties of blackberries, 
dewberries, and red raspberries, in order to determine any varietal or 
specific differences in the hardiness of their roots. But, since many of 
the roots either were dead when received or blackened soon afterward, 
little variation among varieties is recorded. Only one-year plants were 
used. Since the one-year roots of the black raspberry are so small, and 
injury to them is difficult to detect, no data are given on this species. 

Comparison of the resistance of the blackberry varieties recorded in 
table 7 shows the Eldorado to be apparently the least affected. The roots 
of the Early Harvest and the Watt show about equal tenderness. 



TABLE 7. 



Effect of Low Temperature on the Roots of Blackberry, Dewberry, 
AND Red Raspberry 



Temper- 
ature 
(centi- 
grade) 


Date of 
freezing 


Variety 


Diam- 
eter 
of roots 

(milli- 
meters) 


Num- 
ber of 
roots 


Num- 
ber of 
roots 
unin- 
jured 


Per cent of cells killed in injured 
roots 


Cam- 
bium 


Phloem 


Cortex 


Pith 


Xylem 


— 9° 


March 6 
to 20 


Eldorado 

Watt 

Early 

Harvest 
Lucretia 
Austin 


5x4 
5x4 
6x5 
5x4 
4x3 
5x4 


5 
5 
2 
3 
5 
5 


5 

1 
2 

5 

2 














50 


50 


50 














45 


45 


45 














85 


85 


85 












— 10° 


Eldorado 

Watt 

Early 

Harvest 
Lucretia 
Austin 


3x2 
3x2 

3x2 
3x2 
3x2 


10 
7 

11 
10 
10 


10 

9 
9 
9 














60 

50 
25 
25 


60 

50 
25 

25 


60 

50 
25 
25 


40 
50 
















—11° 


Eldorado 

Watt 

Early 

Harvest 
Lucretia 


5x4 
5x4 

5x4 
5x4 
3x2 


6 

7 

6 
5 

8 


4 
5 

5 
4 
3 


15 
100 

100 
50 
100 


15 
100 

100 

50 

100 


15 
100 

100 

50 

100 








50 






















—12° 


Eldorado 

Watt 

Early 

Harvest 
Lucretia 
Cuthbert 


6x5 
6x5 

5x5 
5x4 
4x4 


12 
10 

5 
8 
6 


i 


100 
100 

100 

75 

100 


100 
100 

100 

75 

100 


100 
100 

100 

75 

100 


20 
20 

35 






100 




— 7° 


March 23 

to 
April 17 


Eldorado 

Watt 
Early 

Harvest 
Lucretia 
Austin 


6x5 
3x2 
3x2 

3x2 
2x1 
2x1 


2 
11 

7 

7 
17 
11 


1 
11 

7 

7 
15 
11 








10 












































25 

















638 



D. B. Carrick 



TABLE 7 (concluded) 



Temper- 
ature 


Date of 
freezing 


Variety 


Diam- 
eter 
of roots 

(milli- 
meters) 


Num- 
ber of 
roots 


Num- 
ber of 
roots 
unin- 
jured 


Per 


cent of cells killed in inj 
roots 


ured 


(centi- 
grade) 


Cam- 
bium 


Phlosm 


Cortex 


Pith 


Xylem 


—7° 


March 23 

to 
April 17 

{concluded) 


Cuthbert 

Perfection 

Loudon 


4x3 
3x2 
4x3 
3x2 


6 
10 
5 

4 


6 


























4 

2 






10 
25 


























— 8° 


Eldorado 

Watt 

Early 

Harvest 
Lueretia 

Cuthbert 

Perfection 
Loudon 


7x2 
3x2 

3x2 
5x5 
3x2 
7x5 
3x2 
5x3 
6x4 
4x2 


4 

7 

6 
3 
20 
3 
3 
5 
4 
4 


4 

7 

6 
3 
14 
3 


















































50 


50 


50 












100 
100 








3 
4 


























50 


















—9° 


Eldorado 
Lueretia 
Cuthbert 
Perfection 


8x8 
5x5 
4x3 
3x2 
5x5 
3x2 
3x2 


3 
8 
10 
4 
4 
3 
4 


1 

9 

2 
2 


70 
60 
25 
20 
100 


20 
60 
25 
20 
100 


20 
60 
25 
20 
100 
100 
90 


50 
30 


■ "35 






















3 


90 


90 












—10° 


Eldorado 
Lueretia 
Cuthbert 
Perfection 


6x5 
3x2 
5x4 
3x2 


9 

8 

6 

10 


1 

2 


95 

55 

100 

100 


100 

55 

100 

100 


95 

55 

100 

100 


100 


60 




















—11° 


Eldorado 

Watt 
Lueretia 
Cuthbert 
Perfection 


6x5 
7x2 
5x4 
5x4 
5x3 
5x4 


10 
2 
3 
6 
9 
7 


i' 


100 
75 

100 
90 

100 

100 


100 
75 

100 
90 

100 

100 


100 
75 

100 
90 

100 

100 


50 

60 

100 

75 


50 

"80 
75 














—12° 


Eldorado 


5x4 


5 




100 


100 


100 


100 


100 



At an exposure of -9° C, three roots out of five of the Austin dew- 
berry were killed while the Lueretia was unhurt. In practically all com- 
parable freezings, the Lueretia seems a trifle hardier than the Eldorado 
blackberry, but the margin of difference is small. 

A comparison of the red raspberry varieties indicates the advantage of 
the Cuthbert root over the Perfection. The number of Loudon roots 
tested was not sufficient to permit comparison. Contrast of the relative 
resistance of Cuthbert as compared with Lueretia suggests the superior 
hardiness of the latter, while Cuthbert has the approximate killing point 
of the Eldorado blackberry. 



Resistance of Roots of Fruit Species to Low Temperature 639 

It is seen from the results given in table 7 that none of this Material 
survived a temperature of -12° C. However, many of the larger roots 
tested at -11° previous to March 20 were uninjured. Their relative 
hardiness, therefore, would place these varieties in the group with the 
Myrobalan plum and the Mazzard cherry. 

resistance of gooseberry and currant roots to low temperature 

The study of the freezing point of gooseberry and currant roots offered 
more difficulty than any other determinations undertaken. During the 
winter of 1915-16 a large amount of currant and gooseberry material 
was tested; in fact, in nearly every freezing a few roots of these species 
were included. Upon examination for injury no appreciable change could 
be observed within the usual time limit. At the end of a still longer period 
between the testing and the examination, no features were exhibited that 
the unfrozen roots did not possess. Owing to the pink or reddish pig- 
ment found in the cells of the cortex, these cells were examined for injury 
under the microscope. At -15° C. no discoloration suggesting injury was 
noted. 

It was accordingly decided to repeat the experiment with the gooseberry 
and the currant roots in a somewhat different way. The varieties were 
restricted to the Downing gooseberry and the Wilder currant. In this 
test, whole two-year plants were root-pruned to about four inches and the 
tops were cut back to four or five branches with three buds left on each. 
The plants thus treated were then placed in the freezing chamber. At 
the same time four-inch pieces of root for microscopic examination were 
tested. After each determination the plants were immediately placed 
in moist sawdust in common storage, where they were allowed to remain 
until May 10. On that date they were planted out in the field. 

Observations on these plants were taken on June 16, and record was 
made of the growth that had taken place up to that time. On August 
4, the observations were repeated, and it was found that no growth had 
taken place in any of the specimens recorded as dead in June. These 
data serve as criteria for the amount of injury that the roots experienced. 
It is clear that this method is less exact than the previous manner of 
determining injury by direct observation. It is not possible, for example, 
to state the size of root affected, or the tissues and the amount of roots 



640 



D. B. Carrick 



killed, except as these facts are expressed by the relative top growth. Still 
this test, supplemented by the microscopic observations, should suggest 
the approximate and comparative resistance of the two species. 

TABLE 8. Effect of Low Temperature on Gooseberry and Currant Roots 

(AprU 3-11, 1917) 



Temper- 
ature 
(centi- 
grade) 


Serial 
num- 
ber 


Variety 


Num- 
ber of 
roots 


Depth 
in soil 
(inches) 


Diameter 
of roots 
(milli- 
meters) 


Results 


—19° 


1 


Wilder 


10 


6-8 


1-6 


5 small leaves present; most of stem 
seemed alive, but growth seriously if 
not fatally delayed 




2 


Wilder 


9 


8-10 


2-6 


1 small yellow leaf appeared; most of 
stem tissues brown 




3 


Wilder 


12 


6-10 


2-6 


No leaves present; stem seemed entirely 
dead thruout 




4 


Downing. . . 


13 


8-10 


1-6 


10 or more small green leaves present; 
stem tissues seemed active 




5 


Wilder 


9 


4-8 


3-6 


Sections examined, 6 mm. and 3 mm. 
Less than 5 per cent of cortex cells 
appeared brown 




6 


Downing . . . 


8 


4 -8 


3-6 


Sections examined, 5 mm. and 3 mm. 
Small root seemed the less affected, 
but 50 per «^t of cortex appeared 
injured in each 


—20.5° 


7 


Downing. . . 


6 


4-8 


3-6 


Sections examined, 6 mm. and 3 mm. 
No cambium injury; at l^ast 50 per 
cent of cortex cells appeared injured, 
with a brownish yellow color 




8 


Downing. . . 


9 


5-8 


1-6 


8 small leaves had developed; slightly 
more injury than in no. 4 




9 


Downing. . . 


9 


6-8 


1-5 


No leaves present; buds and stem 
seemed entirely dead 


—18° 


10 


Wilder 


8 


8 


1-6 


No leaves present; entire top dead as in 
no. 9 




11 


Wilder 


7 


8 


1-6 


Same condition of top as in no. 9 




12 


Wilder 


8 


8 


2-6 


Same condition of top as in no. 9 


—19° 


13 


Wilder 


5 


4^8 


3-6 


Sections examined, 5 mm. and 3 mm. 
Injury less severe than in no. 7 
Downing, but on one side of cortex 
50 per cent of cells killed, on the other 
side 30 per cent injured 


—17° 


14 


Downing . . . 


12 


10 


1-6 


40 or more medium-sized green leaves 
had developed; more vigorous top 
than any of preceding 




15 


Downing . . . 


15 


8 


1-6 


A few less leaves than in no 14, but 
all stem tissues active 




16 


Downing. . . 


15 


8 


2-6 


Practically the same conditions as in 
no. 15 



Resistance of Roots of Fruit Species to Low Temperature 641 



TABLE S ico7icliided) 



Temper- 
ature 
(centi- 
grade) 


Serial 
num- 
ber 


Variety 


Num- 
ber of 
roots 


Depth 
in soil 
(inches) 


Diameter 
of roots 
(milli- 
meters) 


Results 


—17° 

{cone.) 


17 


Downing . . . 


9 


4-S 


1-5 


Sections examined, 5 mm. and 3 mm. 
In small root 25 per cent of cortex 
cells were of a characteristic yellow 
color; large root appeared with 35-40 
per cent injury 




18 


Wilder 


10 


8-10 


2-6 


Not a leaf present; bud and stem dead 
thruout 




19 


Wilder 


6 


10 


1-6 


Complete injury to top as in no. 18 




20 


Wilder 


9 


C-S 


2-5 


Sections examined, 5 mm. and 3 mm. 
85 per cent of cambium, phloem, and 
cortex seemed browned in both large 
and small root; severest injury thus 
far observed 


—18.5° 


21 


Downing. . . 


12 


10 


1-6 


15 or more small green leaves present; 
stem tissues seemed active 




22 


Downing . . . 


15 


8 


1-6 


No leaves developed; buds arid stem 
entirely brown 




23 


Downing . . . 


9 


4-8 


2-5 


Not more than 10 per cent of injury 
in cortex, with no browning in cam- 
bium or phloem cells 




24 


WUder 


10 


10 


1-5 


No leaves present; top still had con- 
siderable live tissue 




25 


Wilder 


10 


8 


1-6 


No leaves developed; buds and stem 
entirely dead 




26 


Wilder 


8 


4-3 


2-5 


Only 5 per cent of cortex cells seemed 
injured, with no browning in other 
tissues 


—18° 


27 


Wilder 


18 


4-8 


1-6 


12 leaves present, ranging in size from 
1 to 4 cm. wide 




28 


Wilder 


14 


8 


2-6 


No leaves developed; whole top com- 
pletely dead 




29 


Wilder 


15 


8 


2-5 


No leaves present; small amount of live 
cortex and phloem appeared in one 
stem 




30 


Downing . . . 


7 


4-8 


2-6 


25 or more medium-sized leaves; all 
stem tissues active 




31 


Downing . . . 


11 


6-9 


1-6 


A few less leaves present than in no. 30; 
otherwise the same 


—16.5° 


32 


Wilder 


9 


4-8 


1-5 


No leaves developed; top appeared dead 
thruout 




33 


Wilder 


13 


6-12 


1-6 


No leaves developed; considerable active 
stem tissue 




34 


Downing . . . 


11 


4-8 


1-6 


8 leaves present; all stem tissues seemed 
alive 




35 


Downing. . . 


15 


4r8 


1-6 


12 leaves present; no dead tissue in 
the top 



642 D. B. Carrick 

From an examination of numbers 1, 2, 3, and 4 in table 8, the goose- 
berry seems slightly hardier than the currant. The microscopic examina- 
tion of numbers 5 and 6, however, are not in accord with the field test. 
While the roots sectioned were kept for four days under the bell jar before 
examination, it is possible that the currant, at least in this case, may 
offer another instance of delayed death after freezing. 

In the next test no currants were included. One Downing survived a 
temperature of -20.5° C. but, since one was killed completely, this 
minimum would probably be near the limit of the gooseberry's hardiness 
at this season. However, microscopic observations showed no more cell 
injury than in material exposed to -19°. 

In numbers 10 to 20, considerable evidence is presented to show a greater 
resistance in the gooseberry root than in the currant. The microscopic 
examination also bears this out. Further examination of the data from 
numbers 27 to 35 gives additional proof of the gooseberry's superior hardi- 
ness. But in the last determination the increase in tenderness of the 
gooseberry is noticeable. 

One point especially to be remembered in regard to this table is the date 
of freezing. On comparing the killing temperature of all of the roots in 
the other species considered, the relative resistance of the currant and the 
gooseberry, particularly the latter, is very obvious. These differences 
represent a range of from five to ten centigrade degrees below the killing 
temperature of the other roots. 

SAP CONCENTRATION OF AMERICAN AND FRENCH APPLE SEEDLINGS AND 
WILDER CURRANT AS MEASURED BY THE FREEZING-POINT 
DEPRESSION 

It was thought possible that the wide variation in hardiness shown by 
the roots in the preceding experiments might be due in part to differences 
in the concentration of the cell sap. Consequently an effort was made 
to ascertain the sap concentration of the various species. Unfortunately, 
however, in many cases the sap was found to be very difficult to obtain. In 
the red raspberry, the dewberry, and the grape, respectively, the sap 
tissue from the roots of twenty-five plants when expressed yielded less 
than a cubic centimeter of sap. In other cases sufficient material was 
not available for this determination. 



Resistance of Roots of Fruit Species to Low Temperature 643 



In the few instances reported in table 9, the roots used for each determin- 
ation were first entirely killed by freezing. The concentration was 
determined by means of a Beckmann freezing-point apparatus, and the 
results, expressed as freezing-point depression, are given in table 9 : 



TABLE 9. Sap Concentration in the Roots op American and French Apple Seed- 
lings AND Wilder Currant as Measured by the Freezing-Point Depression 


Date 


Variety 


Depression 


April 25 ' 


American apple roots, upper half 


2.487 


April 25... 






American apple roots, lower half . 


2 214 










May 12 


Wilder currant roots 


2 685 








May 12 


One-year French apple roots stored one 


year 






2.461 


May 12 


Two-year French apple roots 


1 988 







The data in table 9 show a considerable difference in depression between 
the sap of the one- and the two-year-old French apple roots. Indeed, 
these differences indicate a wider variation than actually existed. The 
sap concentration of the two parts of the American apple root may partly 
explain the fact that the upper half of this root usually suffered less injury 
than did the lower half at the same temperature. . A difference in depres- 
sion of 0.273 should certainly be of some significance. The root of the 
Wilder currant proved to have the highest concentration of sap of any 
of the roots tested. It is indeed, the hardiest of these roots. While 
this superior sap concentration is not without meaning, it probably does not 
wholly explain the exceptional resistance of this variety to low temperature. 

EFFECT OF RAPID TEMPERATURE FALL ON THE FREEZING OF APPLE ROOTS 
Pfeffer (1903:235) stated that "resistant plants withstand rapid and 
slow cooling equally well, and it is doubtful whether a rapid fall of tempera- 
ture is more injurious to plants killed by freezing than is gradual cooling." 
Winkler (1913), however, working with Pfeffer, found that various buds 
endure a much lower temperature when the fall is very slow. 

Chandler (1913), testing many kinds of fruit buds and twigs, found the 
rate of freezing to be an important factor in the killing temperature. 



644 D. B. Carrick 

He observed further that the injury by quick cooHng seemed more serious 
when the rapid fall took place in the early part of the freezing period. 
The latter observation is in accord with Muller-Thurgau's (1880 and 1886) 
determinations from which he calculated the size and the time of formation 
of ice masses in the apple and the potato. 

Mix (1916) found that tissue from the trunks of apples killed at a 
temperature several degrees higher when rapidly frozen than when frozen 
more slowly. 

Some data were procured in this study with a view of determining just 
how great a difference in injury there would be between roots cooled 
rapidly and those cooled slowly. An attempt was made also to find out 
whether the severer injury came during the early or the late period of 
freezing. 

In one freezing the temperature of the air surrounding a large number of 
roots, all but a few of which were American-grown apple seedlings, was 
lowered from 1.5° to -4° C. in one hour and forty minutes, and from -4° to 
-8° in twenty minutes, when the roots were removed. In another 
freezing the temperature with the same kind of roots was lowered from 
1.5° to -4° in twenty minutes, and from -4° to -8° in one hour and 
twenty-five minutes, when the roots were removed. It is difficult to draw 
conclusions from but one freezing of each kind, and therefore the data are 
not included. In the second freezing in which the rapid temperature fall 
was at the beginning — that is, from 1.5° to -4° C— the killing was 
slightly the worse, tho a few French seedlings included were not killed as 
badly as in the first freezing. 

Of course it should be borne in mind that the roots in the second freezing 
probably reached a lower temperature than did those in the first. It is 
doubtful whether the roots themselves actually reached the temperature 
of -8° C. in twenty minutes. The results suggest that there is little 
difference in the effect on the killing temperature, whether the rapid 
temperature fall is near the point where freezing begins or nearer the point 
of the kilhng temperature. Many more freezings would be necessary, 
however, before conclusive results could be reached. 

Another set of three freezings was made in order to learn the effect of 
rapid temperature fall on the amount of injury done. In one freezing an 
attempt was made to approach what would be a normal temperature fall, 
the temperature falling from 1.5° to -8° C. in three hours and ten minutes. 



Resistance of Roots of Fruit Species to Low Temperature 645 

In the second freezing the temperature fell from 1,5° to -8° in forty- 
five minutes, when the roots were removed. In the third freezing the 
temperature fell from 1.5° to -8° in fifteen minutes, and the roots were 
held at that temperature for one hour. It is of course probable that in 
the second freezing, in which the roots were removed at once when the 
temperature of the surrounding air had reached -8° C, the tissue of 
the roots never reached that temperature. The injury was certainly the 
least with the slow temperature fall; it was somewhat greater in the second 
freezing, in which the roots were removed at once; and it was markedly 
greater in the third freezing, in which, after the temperature had fallen 
to -8° in fifteen minutes, the roots were held at that temperature for one 
hour. Thus, with the slow temperature fall, of twelve pieces of American 
roots seven had no injury, one had 15 per cent of the cambium browned, 
three had from 30 to 35 per cent of the cambium browned, and one had 
from 50 to 80 per cent of the cambium browned; in the second freezing, 
in which the roots were removed immediately after the temperature had 
reached -8° C. in forty-five minutes, of fourteen pieces of American- 
grown apple roots five were uninjured, one was very slightly injured, 
three had from 10 to 20 per cent of the cambium browned, with slight 
injury to the phloem and the cortex, one had 25 per cent of injury in these 
tissues, three had from 50 to 75 per cent of injury, and one was apparently 
killed thruout; in the case of the third freezing, in which the roots were 
held at -8° C. for one hour after the surrounding air had dropped to 
that temperature in fifteen minutes, of nineteen pieces of American-grown 
apple roots seven showed from 25 to 60 per cent of cambium injury and 
the remainder showed more injury than that, three being killed practically 
thruout. Comparing these last two freezings with the slow freezing, it 
is plain that the rapid temperature fall was the most injurious. In all 
of these freezings careful records were kept as to the resistance of roots 
near the surface and of those that had grown deeper in the soil, and roots 
of the same size showed approximately equal resistance regardless of the 
soil depth from which they came. 

EFFECT OF RATE OF THAWING ON THE FREEZING OF ROOTS 

Goppert (1830) concluded, after many experiments, that the rate of 
thawing had nothing to do with the subsequent injury caused by cold. 
This view was contrary to the popular belief of his time. Sachs (1860) 



646 D. B. Carrick 

st,ated that "the same tissue which, after exposure to freezing temperature, 
with slower thawing remained alive unhurt, becomes disorganized when 
with similar freezing it is thawed rapidly." ^ Miiller-Thurgau (1886) 
pointed out that Sachs' method of placing his tissues in cold water to thaw 
them was really a case of rapid thawing, since a layer of ice formed about 
the tissues, thus releasing considerable heat. Miiller-Thurgau, using 
many plants and plant parts, found that the ripe fruits of the pear and the 
apple, and the leaves of Agave americana L., were injured somewhat less 
when slow thawing was practiced. Molisch (1897) confirmed these results 
of Miiller-Thurgau. Chandler (1913), in his experiments, also found that 
when the temperature did not go too low, slow thawing reduced the 
injury to ripe apple and pear fruits and to lettuce leaves; the rate of thawing 
did not influence the amount of injury to the many other tissues studied. 
In this work several experiments were conducted to determine the 
influence of slow and of rapid thawing on most of the root species used. 
After being lowered to the killing temperature the material was divided 
into four comparable lots. It was then thawed at the following tempera- 
tures: slightly below freezing but gradually rising; at 0° C; at 8° C. 
in the basement storage; and at 22° C in the laboratory. After a number 
of hours all the lots were placed under a bell jar at room temperature. 
Slight differences were noted, but these were confined to very narrow 
limits and seemed to result from an inherent tendency to vary rather than 
to be due to any particular set of thawing conditions. When summarized 
the variations practically canceled themselves and no specific effect could 
be attributed to the rate of thawing. 

INJURY TO APPLE ROOTS WHEN FROZEN IN SOIL, IN WATER, AND IN 

PARAFFIN 

Some determinations were made in which American-grown apple roots 
were placed in the freezing chamber and completely surrounded by a 
garden loam soil. In one case the soil was well dried by exposure to warm 
air. In another case enough water was added to the loam to make it 
rather muddy. A third soil contained a normal amount of moisture. 
Twenty-five roots were used in each treatment, and, except in the case of 
the muddy soil, an effort was made to pack the earth about the roots. In 
a fourth determination water was substituted for the soil. The water 



' Translation from the original German. 



Resistance of Roots of Fruit Species to Low Temperature 647 

came well above the top of the material. When the thermometer and the 
roots were removed after the freezing period, the water was frozen into 
a solid block of ice about them. 

The conditions of these determinations seem too artificial to justify 
the presentation of tables, but the results may be briefly stated. On 
comparing the influence of the different soils with a normal air determina- 
tion, it was found that the roots frozen in air-dried loam were very nearly 
as resistant to cold as were those frozen in the air. The roots treated 
in muddy and normal soil seemed shghtly easier to injure than those 
tested in the air or in the air-dried loam. However, these differences 
were hardly large enough to be dependable, especially when the natural 
tendency of the species to vary is considered. The material surrounded 
by water manifested no constant behavior different from that of the 
other roots. 

Since it was believed that the freezing might not be uniform in such a 
large volume of water, and that severer injury might occur in certain 
areas of the tissue than in other areas due to the presence of air pockets, 
another test was made some weeks later. One resistance thermometer 
was placed in a graduated cyUnder of 100 cubic centimeters capacity; 
a second was placed in water in a large test tube 1| by 5 inches in size; 
and a third was exposed to the air in the chamber. Pieces of apple root 
were placed in large test tubes with and without water. While a large 
quantity of salt and ice was being used, the readings given in table 10 were 
recorded. It is evident from this table that low temperature can be 
temporarily excluded by appropriate quantities of water. After a certain 
period of time, however, such protection becomes ineffective. The length 
of time of such insulation seems to vary with the volume of water used. 

On examining another large test tube taken from the freezing chamber, 
in which were placed three medium-sized apple roots, it was noticed that 
some of the water in the tube was unfrozen. It seems significant also that 
when the roots were examined two days later, not a cell appeared to be 
injured, while the cambium, the phloem, and the cortex tissues of three 
similar roots placed in the air were entirely dead. The water in the gradu- 
ated cylinder in which a thermometer was placed was completely frozen. 

From these facts the effect of the water seems to be due to the unfrozen 
water. When the entire mass becomes ice, it readily conducts the heat 
out of the interior. 



648 

TABLE 10. 



D. B. Carrick 

Influence of Air and Water in Lowering the Temperature Around 
Resistance Thermometers 

(August 4, 1917) 





Temperature (centigrade) 


Hour 


Thermom- 
eter in 

graduated 
cylinder 


Thermom- 
eter in 
large 
test tube 


Thermom- 
eter in 
air 


3 00 


11° 

4.5° 

0° 

0° 

0° 
—0.5° 
—0.5° 
—0.5° 
—0.5° 
—0.5° 
—1° 
—2° 
—7° 
—11.5° 
12° 


13° 
6° 

4.5° 
1° 

0° 
—0.5° 
—0.5° 
—0.5° 
—0.5° 
—0.5° 
—0.5° 
—0.5° 
—1° 
-3° 
—8° 


15° 


3 20 


8" 


3 30 


6.5° 


3 45 


3° 


4 00 


—0.5° 


4 10 


—5.5° 


4 20 


—9.5° 


4 30 


—10.5° 


4 45 


—11° 


5 00 


—11.5° 


5 15 


—11.5° 


5 30 


—12° 


5 45 


— 12° 


6 00 


—12° 


6 15 


—12° 







A rather extensive series of seventy-one tests was conducted, to determine 
whether water or paraffin might be possible factors in influencing the 
amount of injury. The method and results of these tests were as 
follows : 

Apple roots were placed in ordinary test tubes, which were sealed and 
in their turn put into larger test tubes, and the surrounding space was 
filled with water, paraffin, or air. Other apple roots were completely 
coated with melted paraffin and frozen in the usual way, while still others 
were immersed and frozen in test tubes containing water. All the lots 
were given an exposure of from -9° to -12° C. 

In most cases in which water surrounded the tissue but was not in direct 
contact with it, some protection from freezing was afforded as compared 
with material lacking such treatment. As previously noted, the amount 
of protection seemed directly proportional to the volume of water used. 
In the case in which the roots were immediately surrounded by water, 
the protective influence was less pronounced. This may have been due 



Resistance of Roots of Fruit Species to Low Temperature 649 

in part to an increased moisture content of the tissue brought about by 
several hours of exposure in the water. 

Among the roots used in these tests, thirty-six were covered with paraffin 
and were tested at different temperatures. Of these roots, twenty-five 
suffered considerably more injury in the three outer tissues than did the 
corresponding checks, eight seemed to be injured somewhat less than the 
normal, and three showed injury similar to that in the untreated roots. 
The removal of the paraffin immediately after the exposure seemed 
inconsequential. 

The cause for this behavior is not readily apparent, unless, perhaps, 
it may be associated with the phenomenon of supercooling. Accord- 
ing to this hypothesis, the coating of paraffin might have functioned to 
delay ice formation in the tissue by preventing normal inoculation from 
the surface crystals, thus prolonging the supercooling period. The sur- 
rounding air temperature constantly being lowered, more serious damage 
might have resulted from rapid freezing once ice crystallization began. 

INFLUENCE OF THE SCION ON THE HARDINESS OF ONE-YEAR ROOTS OF 

THE STOCK 

In February, 1916, 640 piece-root apple grafts were made, the varieties 
Tompkins King, Baldwin, Oldenburg, and Mcintosh being used as scion 
wood. These varieties were selected for the scions because of the well- 
known difference in the hardiness of their twigs. The stocks were taken 
from long-rooted American seedlings. Each stock was cut into four 
equal parts, from three to four inches in length. Since the lower pieces 
of a seedling are smaller than the crown cut, each variety was grafted on 
each of the four cuts, in order to exclude any variation from this source. 
This gave sixteen possibilities, each represented by forty plants. The 
column in table 11 headed *' Section of stock " indicates the cut of the 
stock used; for example, section 1 is the crown cut, section 2 is the first cut 
below the crown, and so on. 

This material was planted out rather early and was given average care 
thru the summer. The roots were dug after the leaves had fallen, and were 
placed in common storage until tested. Only the roots that had developed 
in 1916 from the parent stock were used. They were rather abundant 
at the lower callus, and were generally from two to three millimeters in 
diameter. Other roots of the American and French apples were tested 
from time to time for comparison. 



650 D. B. Carrick 

TABLE 11. Influence of the Scion on the Hardiness of One-Yeak Roots of the Stock 



Temper- 
ature 


Date of 
freezing 


Variety 


Section 

of 
stock 


Diam- 
eter 
of roots 

(milli- 
meters) 


Num- 
ber of 
roots 


Num= 
ber of 
roots 
unin= 
jured 


Per cent of cells killed 
in injured roots 


(centi- 
grade) 


Cam- 
bium 


Phloem 


Cortex 


—10° 


February 
21 to 24 


Mcintosh 


1 
4 


3x3 
3x2 


5 
5 


5 
5 










15 














Oldenburg 


3 
4 
4 


3x2 
4x3 
3x2 


5 
5 

8 


4 

5 

8 


































Baldwin 


1 

4 


3x3 
3x3 


5 
5 


5 
5 


























Tompkins 
King 


4 
1 


3x3 
3x2 


8 
5 


7 
5 


50 


50 


50 












American 




3x3 
3x2 


4 
3 


4 

2 












15 


15 




French 




3x2 


4 


4 
















— ir 


February 
17 


Mcintosh 


2 
3 
3 


4x3 
4x3 
3x2 


5 
5 

4 


5 
5 
4 


































Oldenburg 


2 
3 


4x3 
3x2 


5 
10 


5 
10 


























Baldwin 


2 
3 
3 


4x3 
4x3 
3x2 


6 

3 

12 


4 
3 
11 


15 


15 


15 




15 


15 


15 




February 
21 


Mcintosh 


2 


3x2 


13 


10 


25 














Oldenburg 


1 
2 


3x2 
3x2 


7 
8 


5 
4 


25 
30 




















Baldwin 


1 

2 


3x2 
3x2 


13 

8 


13 

5 










25 














Tompkins 
King 


1 

2 


3x2 
3x2 


8 
10 


6 


50 
15 


25 
15 


25 
15 




American 




4x3 


6 


6 


















French 




3x2 


4 


4 

















Resistance of Roots of Fruit Species to Low Temperature 651 

TABLE 11 (continued) 



Temper- 
ature 
(centi- 
grade) 


Date of 
freezing 


Variety 


Section 

of 
stock 


Diam- 
eter 
of roots 

(milli- 
meters) 


Num- 
ber of 
roots 


Num= 
ber .of 
roots 
unin= 
jured 


Per cent of cells killed 
in injured roots 


Cam- 
bium 


Phloem 


Cortex 


—11° 
(cone.) 


March 3 


American 




3x2 


6 


4 


20 


20 


20 


French 




3x2 


6 


4 


:o 


20 


20 


—11.5° 


February 

28 


Mcintosh 


1 
4 


3x2 
3x2 


5 

6 


S 
6 


























Oldenburg 


3 


3x2 


5 




50 


50 


50 




Baldwin 


3 

1 


3x2 
3x2 


5 
3 


I 

3 


50 


50 


50 












Tompkins 
King 


2 


3x3 


5 


2 


40 


40 


40 




American 




3x2 


5 


1 


50 


50 


50 




French 




3x2 


5 




70 


70 


70 


—12° 


February 
17 


Mcintosh 


1 
4 


3x2 
3x2 


5 
6 




100 
100 


100 
100 


100 
90 




Oldenburg 


3 

4 


3x2 
3x2 


6 

7 




60 
70 


60 
70 

70 
90 


60 
70 




Baldwin 


1 
4 


3x2 
3x2 


6 
6 




70 
90 


70 
90 




Tompkins 
King 


1 
3 


3x2 
3x2 


5 

6 




75 
60 


75 
60 


75 
60 




American 




4x3 
3x2 


2 
5 




75 
80 


75 
80 


75 

80 




French 




4x3 
3x2 


2 
5 




90 
100 


90 
100 


90 
100 




February 
26 


Mcintosh 


2 
3 


4x3 
4x3 


5 
5 




60 
80 


60 

80 


60 
80 




Oldenburg 


2 


4x3 


6 


3 


20 


20 


20 




Baldwin 


2 
3 


4x3 
4x3 


5 
5 




100 

85 


100 

85 


100 

85 



652 



D. B. Carrick 

TABLE 11 (concluded) 



Temper- 
ature 
(centi- 
grade) 


Date of 
freezing 


Variety 


Section 

of 
stock 


Diam- 
eter 
of roots 

(milli- 
meters) 


Num- 
ber of 
roots 


Num= 
ber of 
roots 
unin= 
jured 


Per cent of cells killed 
in injured roots 


Cam- 
bium 


Phloem 


Cortex 


—12° 
(cone.) 


February 
26 

(concluded) 


Tompkins 
King 


2 
3 


4x3 
4x3 


5 
5 




80 
45 


80 
45 


80 
45 




American 




4x3 


5 




70 


70 


70 




French 




4x3 


4 




100 


100 


100 




March 
1 to 3 


Mcintosh 


1 

2 

3 


3x2 
3x2 
3x2 


5 

10 

5 




100 

60 

100 


100 

60 

100 


100 

60 

100 




Oldenburg 


1-4 
2 
3 


3x2 
3x2 
3x2 


12 
5 

7 


2 

i 


55 

80 
70 


55 
80 
70 


55 

80 
70 




Baldwin 


1 

3 

3-4 


3x2 
3x2 
3x2 


5 

3 

11 


i 


70 

85 
70 


70 

85 
70 


70 
85 
70 




Tompkins 
King 


1-3 
2 
3 


3x2 
3x2 
3x2 


11 
6 
6 




90 
90 
70 


90 
90 
70 


90 
90 
70 




American 




3x2 


18 




70 


70 


70 




French 




3x2 


14 




70 


70 


70 



The results shown in table 1 1 require but little comment. At a tempera- 
ture of -10° C, as was expected, only a negligible amount of injury 
occurred in any roots. Likewise at -11° most of the root tissues escaped 
severe browning. An exposure to -12°, however, resulted in serious 
injury in practically all the roots tested. The temperature of -11.5° 
suggests a point below which most of the roots are killed, and above which 
little or no injury takes place in any variety. 

The above observations are limited in extent and might not apply to 
other conditions. However, an analysis of these particular data seems 
to indicate strongly, not only that the size of the section of root used for 
the stock has no influence on the freezing point of the new roots, but also 



Resistance of Roots of Fruit Species to Low Temperature 653 

that there are no constant nor considerable differences in hardiness of the 
roots developed from any of the four different varieties. It is shown 
further that there is no significant variation in the hardiness of the grafted 
and the seedling stock. 

EFFECT OF SUGAR SOLUTIONS, WATER, AND DRYING OUT, ON THE 
RESISTANCE OF APPLE ROOTS TO FREEZING 

Since a number of investigators have found that certain solutions have 
various influences on plant tissue with reference to freezing resistance, data 
were procured to ascertain whether or not similar effects could be observed 
in the roots. Before consideration of table 12, containing these data, 
it seems well to briefly mention some of the results reported regarding the 
influence of moisture content and the concentration of cell sap on the 
freezing to death of plant tissue. 

It is well known that air-dried seeds can resist a very low temperature, 
but if allowed to absorb water they are frozen rather easily. Miiller- 
Thurgau (1880) found that succulent tissue has a higher freezing point 
than material with a lower moisture content. Shutt (1903), Selby (1908), 
Shaw (1911), and Beach and Allen (1915) seemed to find that apple twigs 
are tender in proportion to the higher moisture content. Mix (1916), 
on the contrary, reported that tissue from the trunk of apple trees soaked 
in distilled water for an hour and then frozen was not injured more than 
normal untreated material. 

Bartetzko (1910) found that Aspergillus, Penicillium, and other fungi 
grown in nutrient solutions of varying concentration, increased their 
resistance to freezing in proportion to the increase in the osmotic strength 
of the solution. Ohlweiler (1912) observed that in species of Magnolia 
in which the cell structure of the leaves was essentially the same, the 
concentration of sap was an indication of the relative hardiness of the 
species. Chandler (1913:181) stated, in summarizing his experience in 
connection with the relation of sap concentration to hardiness, " In case 
of plants not in a resting condition, a large amount of dissolved material 
either' in the sap within the cell or in a solution surrounding the cell, will 
protect the cell from injury due to low temperature, to some extent at 
least." Chandler noted also that apple roots kept in water for eighteen 
hours were more severely injured than similar material dried in the air 
for the same period. 



654 



D. B. Carrick 



Maximow (1914) studied at length the influence of several organic and 
mineral solutions on the protection of red cabbage and tradescantia cells 
from cold. He found marked protection from these compounds, except 
when the solution was of a toxic nature or when it precipitated its solutes 
at a temperature near the freezing point of the cell sap. Not all of the 
increased cold resistance, however, was explained by the differences in the 
depression of the freezing point of the sap. 

In these observations (table 12) the concentration of the cane sugar 
solutions to which the apple roots were exposed varied from 0.1 gram 
to 3 grams molecular. The length of exposure ranged from twenty minutes 
to ninety-six hours. Similar treatment was given using tap water instead 
of a sugar solution. In no cases were the roots frozen in the solutions, 
as in Maximow's (1914) experiments, and the free surface moisture was 
always removed. The roots were allowed to dry out at storage or laboratory 
temperature for from fourteen to sixty-eight hours. In a few instances 
both the drying-out and the solution treatment were given the same root. 



TABLE 12. 



Effect of Various Previous Treatments on the Freezing to Death of 

American Apple Roots 



Temper- 
ature 


Date 

of 

freezing 


Previous treatment 


Average 
diameter 
of roots 
(milli- 
meters) 


Num- 
ber of 
roots 


Num- 
ber of 
roots 
unin- 
jured 


Per cent of cells killed 
in injured roots 


(centi- 
grade) 


Cam- 
bium 


Phloem 


Cortex 


— 8° 


April 28 




7x6 

7x7 
8x7 
6x6 

7x6 

8x6 


4 

7 
3 
2 

7 

3 


7 

1 


25 


10 


10 




18 hours at 22° in labora- 






18 hours in tap water. . . . 


50 
70 

55 

15 


40 






18 hours in 0.1 gram cane 


20 
10 






18 hours in 0.05 gram 










— 9° 


May 
1 to 2 




7x6 

7x7 
7x6 

8x6 
6x5 
7x7 
7x6 

7x6 

8x7 
7x7 

8x7 
8x7 


16 

2 
4 

•7 
6 
4 

4 

4 

4 
6 

4 
4 


5 

1 
3 

6 
5 

1 


60 

40 
10 

10 

65 

100 

100 

100 

100 
80 

70 
100 


20 


15 




18 hours at 8° in store- 






44 hours as above 

44 hours at 22° in labora- 


10 

10 

65 

100 

100 

100 

100 
70 

35 
90 






68 hours as above 

44 ho irs in tap water. . . . 

68 hours as above 

68 hours in 0.1 gram cane 


65 
100 
100 

100 




41 hours in 0.2 gram cane 


100 




68 hours as above 

41 hours in 0.1 gram salt 

solutioi 

68 hours as above 


60 

5 
80 



Resistance of Roots of Fruit Species to Low Temperature 655 

TABLE 12 (concluded) 



Temper- 
ature 
(centi- 
grade) 






Average 




Num- 


Per cent of cells killed 


Date 




diameter 


Num- 


ber of 


in injured roots 


of 
freezing 


Previous treatment 


of roots 
(milli- 


ber of 
roots 


roots 
unin- 








Cam- 
bium 










meters) 




jured 


Phloem 


Cortex 


—10° 


May 


Untreated 


7x6 


23 


5 


65 


30 


20 




5 to 10 


48 hours at 8° in store- 


















room 


7x6 


5 


3 


10 








48 hours at 22° in labora- 










tory 


7x7 

7x7 


2 
2 


2 










24 hours in tap water .... 


100 


100 


100 






48 hours as above 


7x6 


8 




90 


90 


85 






24 hours in 0.5 gram cane 


















sugar solution 


7x6 


2 




100 


100 


100 






48 hours as above 


7x7 


4 




100 


100 


100 






72 hours in 0.5 gram cane 


















sugar solution; 16 hours 


















at 22° in laboratory. . . . 


6x5 


3 


1 


65 


50 


50 






20 minutes in 1 gram cane 




















7x7 
7x6 


2 

2 


2 










24 hours as above 


100 


100 


100 






48 hours as above 


7x7 


4 




75 


75 


75 






72 hours as above 


7x7 


4 




80 


80 


80 






96 hours as above 


6x5 


5 




100 


100 


100 






72 hours in 1 gram cane 


















sugar solution; 16 hours 


















at 22° in laboratory . . , 


6x5 


5 


1 


75 


60 








20 minutes in 2 grams cane 




















7x7 
7x6 


2 
4 


2 










24 hours as above 


100 


100 


100 






48 hours as above 


7x7 


4 




75 


75 


75 






72 hours as above 


6x5 


2 




100 


100 


100 






76 hours as above 

72 hours in 2 grams cane 


9x8 


1 


1 




















sugar solution; 16 hours 


















at 22° in laboratory. , . . 


7x6 


5 


1 


90 


55 


50 






20 minutes in 3 grams cane 


















sugar solution 


7x7 


2 




100 


100 


100 






48 hours as above 


7x7 


7 




100 


100 


90 






72 hours as above 


6x5 


2 




100 


100 


100 






72 hours as above 


9x8 


4 




100 


45 


30 






72 hours in 3 grams cane 


















sugar solution; 16 hours 


















at 22° in laboratory. . . . 


6x5 


2 




100 


100 


100 






96 hours at 22° in labora- 


















tory; no injury at -10°; 


















then 48 hours in tap 




















8x7 


2 




100 


100 


100 









It is readily seen, in essentially all cases in table 12, that the roots kept 
in cane sugar and salt solutions longer than twenty minutes were injured 
more than the untreated tissue and about the same as the roots placed in 
water. On the other hand, roots dried in the air at 8° and 22° C. exhibited 
less killing than the normal tissue. These conclusions seem true regardless 
of the freezing temperature used, the time exposure above eighteen hours, 
or the concentration of the solution employed. The few roots exposed for 
twenty minutes in sugar solution did not decrease in resistance. More 



656 D. B. Carrick 

examples are necessary, however, before these data can be considered 
dependable. 

An interesting fact brought out in this connection is the effect of drying 
after exposure to a sugar solution. While the roots scarcely recovered 
normal hardiness in most instances, the percentage of injury was somewhat 
lessened except when small roots were employed. In the last case shown 
in table 12, two roots exposed to -10° C. without injury were killed thruout 
after remaining in tap water for forty-eight hours. 

Unfortunately, at the time of this study not enough material was 
available to determine the freezing-point depression of the sap of the roots 
kept in sugar solutions. If the sap concentration was increased by such 
treatment, another factor, or other factors, inhibited its action in lowering 
the freezing point of the tissue. 

According to table 9 (page 643) the depression of the American-grown 
apple root would indicate a concentration of about 1.33 gram molecular. 
Since the concentration of the sugar solutions ran as high as 3 grams 
molecular, either plasmolysis or an increase in the concentration of cell 
sap would be expected. To determine this point, sections of roots exposed 
to the various concentrations used in the experiment just described were 
examined under the microsope. In all cases the cells appeared normally 
turgid. 

The cause of the severer injury to cells of higher moisture content, while 
often observed, is also rather obscure. It seems, however, that if both the 
moist and the dry tissues possessed the same initial concentration, at an 
air temperature of -9° or -10° C. both should possess the same amount 
of water in the cells, regardless of the injury. Indeed, both have given up 
the identical amount of water at -10° C, the dry root having lost its 
water thru evaporation and ice formation, the moist root thru ice formation 
only. This reasoning suggests that the greater injury in the moist cells 
may be due to a larger ice mass formed in them. It suggests further that 
causes other than dehydration must account for the phenomenon of 
freezing to death of plant tissue. 

SUMMARY 

There is little difference in hardiness of the roots between American and 
French apple seedlings. Normal one-year roots are hardier than one-year 
stocks held one year in cold storage or grown in the field a second year. 



Resistance of Roots of Fruit Species to Low Temperature 657 



Temperature 
(centigrade). 



—20.5"- 



— 18»- 



—15.5° 



—15°- 



-14.5°- 



—12° 



— 11° to— 12*'- 



-11»- 



—10° to —11° 



-10"- 



— 8»- 



-T»- 



lO 



8 



T 



Nov. Dec-Jan. Feb.-Mar. Mar. 29-Apr. 15 Apr. 16-May 8 

Fig. 164. seasonal hardiness of fruit roots 

1, Apple (French "crab"), and grape (Lindley, Norton, and Cyiithiana). 2, Pear (Frenrh) and plum 
(Myrobalan). 3, Peach. 4, Cherry (Mazzard). 5, Cherry (Malialeb). <i, Grape (Diamond). 7, Grape 
CliatoD and Concord). 8, Raspberry, blackberry, and dewberry. 9, Currant. 10 Gooseberry 



658 D. B. Carrick 

The state of maturity and the diameter of the roots were the important 
factors in determining the resistance to freezing of all species tested in 
these experiments. 

The French pear stock seems more tender than the Kieffer stock. Both 
roots are less resistant to freezing than is the apple. 

Peach roots on which the variety Elberta had been budded proved les? 
hardy than the apple and about equal to the Kieffer pear. 

The order of hardiness of the four cherry stocks tested is as follows: 
Mahaleb, Prunus Besseiji, Primus pennsylvanicum, Mazzard. The 
Mahaleb stock is considerably superior to the apple, while the Mazzard 
is about equal to the French pear. 

Myrobalan plum roots are quite as easily killed by low temperature as 
are the French pear and the Mazzard cherry. 

In the six varieties of grapes studied, the roots of the Clinton and the 
Concord are as hardy as the root of the Mahaleb cherry. The Diamond 
is slightly less hardy. The roots of the varieties Lindley, Norton, and 
Cynthiana are more resistant than the root of the Mazzard cherry but less 
resistant than the apple root. 

No significant differences are seen between the hardiness of the black- 
berry root and that of the red raspberry root. The Lucretia dewberry, 
however, is slightly less tender than either, and is about equal to the apple 
stock. 

Roots of the Downing gooseberry are more resistant to freezing than 
are Wilder currant roots. The roots of the gooseberry and the currant 
seem much hardier than any other roots examined. 

The freezing-point depression of the Wilder currant sap is greater than 
that of the apple sap. Sap from the upper half of American-grown apple 
roots is of a higher concentration than that from the lower half of 
the same roots. The upper half of the root is also somewhat more 
resistant to cold. 

A rapid fall in temperature is shown to increase the freezing injury in 
apple roots. 

The placing of soils of different moisture content in the freezing chamber 
around the roots causes no appreciable difference in the amount of injury. 

A majority of roots entirely covered with melted paraffin killed more 
severely than did similar untreated roots. 



Resistance of Roots of Fruit Species to Low Temperature 659 

Water, when placed in the same test tube with the root tissue or when 
placed around it in another container, often provides protection against 
a low temperature, until all the water is frozen. 

The hardiness of the scion does not seem to affect the resistance of the 
one-year roots of the apple stock. 

Roots placed in sugar solutions varying in concentration from 0.1 
gram to 3 grams molecular, are injured more easily than are normal roots. 
Roots allowed to absorb moisture for several hours are similarly injured. 

In nearly all cases in which the material was allowed to dry, its resistance 
wai increased. 

The difference in the response to cold of the moist tissue and the dry 
tissue may be due to the smaller ice mass formed in the dry root. 



660 D. B. Carrick 



LITERATURE CITED 

Bartetzko, Hugo. Untersuchungen iiber das Erfrieren von Schimmel- 
pilzen. Jahrb. wiss. Bot. 47:57-98. 1910. 

Beach, S. A., and Allen, F. W., Jr. Correlation of maturity and water 
content with hardiness. In Hardiness in the apple as correlated 
with structure and composition. Iowa Agr. Exp. Sta. Research 
bul. 21 : 181-189. 1915. 

Chandler, W. H. The killing of plant tissue by low temperature. 
Univ. Missouri Agr. Exp. Sta. Research bul. 8: 141-309. 1913. 

Craig, John. Observations and suggestions on the root-killing of fruit 
trees. Iowa Agr. Coll. Exp. Sta. Bul. 44:179-213. 1900. 

Emerson, R. A. Experiments in orchard culture. Nebraska Agr. Exp. 
Sta. Bul. 79:1-33. 1903. 

Cover-crops for voung orchards. Nebraska Agr. Exp. Sta. 

Bul. 92:1-23. 1906. 



Goppert, H. R. Tiber die Warmeentwickelung in den Pflanzen; deren 
Gefrieren und die Schutzmittel gegen dasselbe, p. 1-273. 1830. 

Hedrick, U. p. The grapes of New York, p. 1-564. 1908. 

Macoun, W. T. Winter injury to fruit trees — ten different ways in 
which trees are affected. Canadian Exp. Farms. Rept. 1908 : 1 10- 
116. 1908. 

Maximow, N. a. Experimentelle und kritische Untersuchungen iiber 
das Gefrieren und Erfrieren der Pflanzen. Jahrb. wiss. Bot. 
53:327-420. 1914. 

Mix, a. J. Sun-scald of fruit trees: a type of winter injury. Cornell 
Univ. Agr. Exp. Sta. Bul. 382:233-284. 1916. 

MoLiscH, Hans. Untersuchungen iiber das Erfrieren der Pflanzen, 
1-73. 1897. 

MiJLLER-THURGAu, HERMANN. Ueber das Gefrieren und Erfrieren der 
Pflanzen. I Theil. Landw. Jahrb. 9 : 133-189. 1880. 

Ueber das Gefrieren und Erfrieren der Pflanzen. 



II Theil. Landw. Jahrb. 15:453-610. 1886. 

Ohlweiler, William Woodward. The relation between the density of 
cell saps and the freezing points of leaves. Missouri Bot.Gard. 
Ann. rept. 23:101-131. 1912. 



Resistance of Roots of Fruit Species to Low Temperature 661 

Pfeffer, W. Freezing and cold-rigor. In The physiology of plants, 
vol. 2, p. 232-247. (English translation by Alfred J. Ewart.) 
1903. 

Russell, W. De la survie des tissues vegetaux apres le gel. Acad. Sci. 
[Paris]. Compt. rend. 158:508-510. 1914. 

Sachs, Julius. Krystallbildungen bei dem Gefrieren iind Veranderung 
der Zellhaute bei dem Aufthauen saf tiger Pflanzentheile. Kon. 
Sachs. Gesell. Wiss. Leipzig, Math-Phys. CI. Ber. Verb. 12 : 1-50. 
1860. - 

Selby, a. D. Fall and early winter injuries to orchard trees and shrubbery 
by freezing. Ohio Agr. Exp. Sta. Bui. 192:129-148. 1908. 

Shaw, J. K. Climatic adaptations of apple varieties. Massachusetts 
(Amherst) Agr. Exp. Sta. Ann. rept. 23 : 177-245. (Reference 
on p. 181.) 1911. 

Shutt, Frank T. On the relation of moisture-content to hardiness, in 
apple twigs. Roy. Soc. Canada. Proc. and Trans. 2d ser:9: 
sec 4:149-153. 1903. 

Winkler, Albert. Uber den Einfluss der Aussenbedingungen auf die 
Kalteresistenz ausdauernder Gewachse. Jahrb. wiss. Bot. 52: 
467-506. 1913. 



Memoir 33, The Ribbed Pine-Borer, the third preceding number in this series of publications, was 
mailed on August 25, 1920. 



Memoir 36 



Plate TX 





o 



J 



FREEZING INJURY IN ROOTS OF SOME FRUIT SPECIES 

1, Apple. 2, European pear; 3, Kieffer pear. 4, Elberta peach 



3477-110 
Xot 99 



Mkmoir Sfi 



Plate X 



c 







J) 

Q 




n 








FREEZING INJURY IN ROOTS OF SOME FRUIT SPECIES 

1 Morello cherry; 2, Mahaleb cherry. 3, Myrobalan plum. 4, Concord grape 5, Red 
raspberry. 6, Gooseberry, uninjured after fifteen hours exposure at -11 U. 



f'M 


0^ 




"o 


V^ 




^^. 




^^ 




^^ 


'^ 


% ^-^^ J> , 


• ' 


•°', 


*^ 


E 




m 


&\ 



^ 







o V' 



V 



^ 
























"-^^0^ 



C" * 




o 






'bV" 



^°-'^. 







'=^^ ** 
% 













^^--^^ V 













5^5^ 















0" . 
















<?■. " e H - < 



















MAC 7a ♦«/??^=^' ^j' ^ •,ssS5JVk'- *■' 









.<&^ 



^.^' 






